Locking devices are known that comprise a housing, a hook that is cantilevered out from a rocking axis carried by the housing, and a retractable locking member for opposing rocking movement of the hook when the hook is loaded. This type of locking device is used, in particular, for locking a door or a flap in its closed position. In some cases, in particular when the device is used for locking the thrust-reversing flaps of aircraft jet engines, it is necessary for the locking to be provided particularly reliably since failure of the locking device could have extremely severe consequences. In particular, with thrust-reversing flaps for aircraft engines, untimely opening of the flaps in flight or during landing prior to the wheels running on the ground, gives rise to a breaking force on the aircraft such that control of the aircraft is lost irremediably.